The invention relates to an improved method of producing binary self condensation products of phenols. It is well-known in the art that substituted phenols can be oxidized to yield self-condensation products, especially diphenoquinones, biphenols and polyphenylene oxides. The diphenoquinones are useful antioxidants. Biphenols are useful antioxidants, stabilizers and intermediates for the synthesis of various polymers, especially polyesters. Polyphenylene oxides comprise a useful class of polymeric materials having utility as molding resins, extrusion resins, etc.
In U.S Pat. No. 4,195,189, a one-step process for the oxidative coupling of phenols is described wherein molten phenols are combined with an oxidizing agent which is activated copper oxide. The copper oxide was employed in about equal or greater molar ratio with the phenolic compound. In this process the copper oxide is employed not as a catalyst but as a source of oxygen as no oxygen or oxygen-containing gas is otherwise present during the reaction.
In German Pat. No. 536,277, the oxides of copper, manganese and lead were employed in the oxidative reaction of phenol. The reaction product was most probably a polymeric material, however was not identified. The product was a light grey amorphous precipitate without a sharp melting point which sintered to a brown mass at 120.degree. C. to 130.degree. C. Diphenoquinone is a highly colored crystalline material which decomposes at about 165.degree. C. Polyphenylene oxide in its higher molecular weights is a tough white solid that has glass transition temperatures in excess of 200.degree. C.